Joint resurfacing operations require the removal or resection of outer layers of bone, some or all of which may be diseased or degraded, in order to allow the implantation of a resurfacing prosthesis. The resurfacing prosthesis includes a bone engaging surface, that contacts and may be cemented to the exposed bone surface, and a bearing surface, designed to articulate with an adjacent natural or artificial bearing surface. In order to ensure correct operation of the reconstructed joint, the bearing surface of the resurfacing prosthesis must be in the correct anatomical position relative to the adjacent structures. To promote stability of the reconstructed joint, it is important that the bone engaging surface of the implant matches closely the resected surface of bone onto which it will be secured. It is also desirable to achieve a smooth transition from prosthesis to bone surface at the edges of the implant. The smoothness of this transition is determined by the accuracy of the resection of the existing bone surface.
The patellofemoral joint is an example of a natural joint that may be resurfaced by implantation of a distal femoral prosthesis. Existing resurfacing operations for this joint require the free hand resection of the distal femur. Resection is normally accomplished by drawing around a template and using an osteotome or rasp to remove the bone. However, the bone engaging surface of a distal femoral prosthesis is a complex surface that varies in three dimensions. It is not possible to replicate such a surface using free hand tools, and hence such conventional methods do not enable a surgeon to achieve a perfect fit between resected bone surface and prosthetic implant. In addition, the free hand removal of a significant area of bone is highly surgically demanding.